Grease composition for constant velocity joint and constant velocity joint

ABSTRACT

A grease composition which provides, in the working range of 150° C. to −40° C., an enhanced temperature control performance, a reduced low-temperature rotational torque and an improved boot resistance; and a constant velocity joint wherein the grease composition is filled; are provided. A grease composition for a constant velocity joint comprising the following components (A) to (E):
         (A) a base oil containing 10 to 95% by mass of an ester synthetic oil produced from an aliphatic alcohol and an aromatic carboxylic acid and 90 to 5% by mass of a synthetic hydrocarbon oil;   (B) a thickener;   (C) molybdenum disulfide;   (D) molybdenum dialkyldithiocarbamate e; and   (E) zinc dithiophosphate.

TECHNICAL FIELD

The present invention relates to a grease composition which reduces thelow-temperature rotational torque and which provides an improved bootresistance, heat resistance and temperature control performance, and toa constant velocity joint wherein the grease composition is filled. Moreparticularly, the present invention relates to a grease compositionwhich provides improved high-speed durability of a constant velocityjoint, a reduced low-temperature starting rotational torque, an enhancedboot resistance due to improvement of the swelling property of rubberand an improved temperature control performance, and to a constantvelocity joint wherein the grease composition is filled.

BACKGROUND ART

Today, in the automotive industry, production of FF vehicles areincreasing from the view points of weight saving and sufficiency of theinterior space. Further, 4WD vehicles are also increasing from the viewpoint of their functionality. In these FF vehicles and 4WD vehicles,transmittance of power and steering is attained with front wheels, sothat, in order to attain smooth transmittance of the power even, forexample, in the state where the steering wheel is fully turned, a driveshaft composed of a constant velocity joint capable of transmittingrotational movement at a constant rate irrespective of various changesin the crossing angle between the two crossing axes is used.

On the other hand, FR vehicles and 4WD vehicles have a structure whereinthe power from the engine is transmitted to the drive shaft for rearwheels through a propeller shaft which is known to act as a source andchannel for transmission of noise and vibration. In place of a propellershaft composed of conventionally used Cardan joint and a sliding spline,a propeller shaft composed of a constant velocity joint capable ofsliding axially while rotating at a constant rate at an operating angleis now becoming widely used.

Since, in recent years, performance improvement of automobiles is beingincreasingly promoted and high-powered automobiles are increasing, theload on the constant velocity joint is also increasing, so that there isa tendency that its lubrication condition becomes severer. On the otherhand, there is also a tendency that improvement of vehicle ride qualityis more and more highly demanded.

Especially, although the load torque on a propeller shaft is lower thanthat on a drive shaft, the operating condition of a propeller shaft isdifferent from that of a propeller shaft: for example, a propeller shaftis used with faster rotation. Therefore, the grease used for a constantvelocity joint is required to exhibit improved high-speed performancesuch as high-speed durability and low vibration at high speed.

The amount of heat (amount of rise in temperature) generated uponrotation of a constant velocity joint may be employed as an index forits high-speed performance, which amount of rise in temperature enablesexpectation of the critical operating condition. Since the amount of theheat generated tends to depend on the friction coefficient of thegrease, development of a grease which exerts an excellent temperaturecontrol performance at high temperature is desired.

On the other hand, smooth operation of a constant velocity joint in anextremely cold region is also considered to be important. In anextremely cold region, an automobile may need to be started in a coldcondition. In such a condition, it is important to reduce thelow-temperature rotational torque of the grease in order to start theautomobile smoothly.

However, a grease composition for a constant velocity joint, whichgrease composition has an excellent temperature control performance anddurability and enables sufficient reduction of the low-temperaturerotational torque, has not been proposed yet.

Conventionally, as the lubricant, a grease composition for a constantvelocity joint, which grease composition containing a base oil, a diureathickener and, as an additive, a molybdenum compound, has been proposed(see, for example, Patent Documents 1, 2, 4, 5, 7 and 8).

A grease composition containing a grease composed of a specifictrimellitate and a thickener, in which grease a compound having a sulfuratom is included, has also been proposed (see, for example, PatentDocument 3).

The rotational resistance of a constant velocity joint of an automobileis largely affected not only by the internal resistance of the constantvelocity joint but also by the hardness of the boot. Especially, at lowtemperature, increase in the starting torque and the rotationalresistance lead to decrease in operability in terms of steering and thelike. In a constant velocity joint having, for the purpose of keepingthe rotational resistance of the constant velocity joint low, a boot forpreventing grease leakage from the inside of the constant velocity jointand invasion of foreign matters, silicone rubber and chloroprene rubberboot materials satisfying the conditions of not more than 55 at normaltemperature (25° C.) and not more than 85 at low temperature (−40° C.)according to JIS K 6253 durometer hardness A type have been proposed(see, for example, Patent Document 6).

However, performances of these grease compositions for constant velocityjoints are insufficient in terms of the temperature control performanceand the performance for decreasing the low-temperature rotationaltorque, so that an improvement to achieve more stable performance isdesired. Further, in cases where a silicone rubber, chloroprene rubberor the like is used as a boot material, performances such as oilresistance, flex resistance, water resistance, weather resistance, heatresistance and cold resistance are demanded, but there has not yet beena proposal of a grease composition useful for achieving a longeroperating life of these various rubber boot materials.

Patent Document 1 JP 10-273691 A

Patent Document 2 JP 10-273692 A

Patent Document 3 JP 11-131082 A

Patent Document 4 JP 2001-11481 A

Patent Document 5 JP 2003-165988 A

Patent Document 6 JP 2005-214395 A

Patent Document 7 JP 2005-226038 A

Patent Document 8 JP 2006-16481 A

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a grease compositionwhich enhances the temperature control performance of a constantvelocity joint, reduces the low-temperature rotational torque andimproves the boot resistance in the working range of 150° C. to −40° C.

Another object of the present invention is to provide a constantvelocity joint wherein the above grease composition is filled.

Means for Solving the Problems

The present inventors intensively studied to achieve the above objectsto discover that a grease composition containing specific components maycontrol generation of heat from a constant velocity joint, reduce thelow-temperature rotational torque and improve the boot resistance in theworking range of 150° C. to −40° C. The grease composition of thepresent invention for a constant velocity joint was completed based onthis discovery.

That is, the present invention provides the following grease compositionfor a constant velocity joint and a constant velocity joint.

1. A grease composition for a constant velocity joint, which greasecomposition comprises the following components (A) to (E):

(A) a base oil containing 10 to 95% by mass of an ester synthetic oilproduced from an aliphatic alcohol and an aromatic carboxylic acid and90 to 5% by mass of a synthetic hydrocarbon oil;

(B) a thickener;

(C) molybdenum disulfide;

(D) molybdenum dialkyldithiocarbamate; and

(E) zinc dithiophosphate.

2. The grease composition for a constant velocity joint, according tothe above item 1, wherein the synthetic hydrocarbon oil of the component(A) is a poly-α-olefin.3. The grease composition for a constant velocity joint, according tothe above item 1 or 2, wherein the ester synthetic oil of the component(A) is produced from a C₆-C₂₂ aliphatic alcohol and a C₈-C₂₂ aromaticcarboxylic acid having 2 to 6 carboxyl groups.4. The grease composition for a constant velocity joint, according toany one of the above items 1 to 3, wherein the thickener of thecomponent (B) is a urea compound.5. The grease composition for a constant velocity joint, according toany one of the above items 1 to 4, wherein each of the contents ofmolybdenum disulfide of the component (C), molybdenumdialkyldithiocarbamate of the component (D) and zinc dithiophosphate ofthe component (E) is 0.1 to 10% by mass based on the total mass of thegrease composition.6. A constant velocity joint wherein the grease composition according toany one of the above items 1 to 5 is filled.

EFFECTS OF THE INVENTION

The grease composition of the present invention enhances the temperaturecontrol performance of a constant velocity joint, reduces thelow-temperature rotational torque and improves the boot resistance inthe working range of 150° C. to −40° C. Therefore, faster rotation of apropeller shaft becomes possible, and an automobile may be started undera low temperature condition, enabling to avoid a trouble in the constantvelocity joint in an extremely cold region.

Furthermore, the grease composition of the present invention reducesdeterioration of a boot material, so that a longer life thereof may beachieved.

The grease composition of the present invention may be used morepreferably for a cross groove constant velocity joint which isespecially suitable for reducing backlash at high speed rotation.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The present invention will now be described in more detail.

The grease composition of the present invention for a constant velocityjoint is characterized in that it contains the above components (A) to(E) as indispensable components. Each of these components will now bedescribed.

The base oil used in the present invention containing 10 to 95% by massof an ester synthetic oil and 90 to 5 weight percent of a synthetichydrocarbon oil may also be a mixture with other synthetic oils and/ormineral oils. Examples of the other synthetic oils include ethersynthetic oils such as alkyl diphenyl ether and polypropylene glycol;silicone oils and fluorinated oils.

Preferred examples of the synthetic hydrocarbon oils used for thecomponent (A) include poly-α-olefins and polybutenes.

The ester synthetic oils used for the component (A) are ester syntheticoils which may be produced from a C₆-C₂₂, preferably C₆-C₁₀ aliphaticalcohol and a C₈-C₂₂, preferably C₈-C₁₂ aromatic carboxylic acid having2 to 6 carboxyl groups. Specific examples of the C₆-C₂₂ aliphaticalcohol include aliphatic alcohols such as 1-hexanol, 2-hexanol,3-hexanol, 1-heptanol, 4-methyl-2-pentanol, 2-heptanol, 3-heptanol,1-octanol, 2-octanol, 2-ethyl-1-hexanol, 1-nonanol, nonane-2-ol,3,5,5-trimethyl-1-hexanol, 1-decanol, 1-undecanol, lauryl alcohol,myristyl alcohol, cetyl alcohol, 14-methylhexadecane-1-ol, stearylalcohol, oleyl alcohol, 16-methyloctadecanol, icosanol, isodecylalcohol, 18-methylnonadecanol, 18-methylicosanol, docosanol,20-methylhenicosanol and 2-octyldodecanol.

Preferred among these are 1-hexanol, 2-ethyl-1-butanol, 1-octanol,1-heptanal, 2-octanol, 2-ethyl-1-hexanol, nonane-2-ol,2-ethyl-1-octanol, isodecyl alcohol and 2-octyldodecanol.

Specific examples of the C₈-C₁₂ aromatic carboxylic acids having 2 to 6carboxyl groups include phthalic acid, isophthalic acid, terephthalicacid, 5-methylisophthalic acid, 4,5-dimethoxyphthalic acid, hemimelliticacid, trimellitic acid, trimesic acid, mellophanic acid, prehnitic acid,pyromellitic acid and mellitic acid.

Preferred among these are 5-methylisophthalic acid, trimellitic acid andpyromellitic acid.

Specific examples of the ester synthetic oils produced from the abovealiphatic alcohol and aromatic carboxylic acid include hexyl phthalate,2-ethylbutyl phthalate, octyl phthalate, heptyl phthalate, 2-octylphthalate, 2-ethylhexyl phthalate, nonane-2-ol phthalate, 2-ethyloctylphthalate, nonane-2-ol isophthalate, 2-ethyloctyl isophthalate, octyl5-methyl isophthalate, nonane-2-ol 5-methyl isophthalate, hexylterephthalate, octyl terephthalate, hexyl trimellitate, octyltrimellitate, heptyl trimellitate, 2-ethylbutyl trimellitate,2-ethylhexyltrimellitate, nonane-2-ol trimellitate, isodecyl alcoholtrimellitate, octyl benzenetetracarboxylate, heptylbenzenetetracarboxylate, hexyl benzenetetracarboxylate, 2-ethylbutylbenzenetetracarboxylate, 2-ethyloctyl benzenetetracarboxylate and2-octyldodecanol pyromellitate. All of these esters are full esterswherein all the carboxylic acids are esterified.

In the base oil of the present invention, the total amount of the estersynthetic oils and the synthetic hydrocarbon oils of the component A isnot less than 40% by mass, preferably not less than 60% by mass, morepreferably not less than 80% by mass and most preferably 100% by mass,based on the total base oil.

Preferred examples of the thickener of the component (B) used in thepresent invention include diurea thickeners represented by the followingGeneral Formula (I).

R¹NH—CO—NH—C₆H₄-p-CH₂—C₆H₄-p-NH—CO—NHR²  (1)

wherein R¹ and R² may be the same or different and may be C₈-C₂₀,preferably C₈-C_(is) alkyl; C₆-C₁₂, preferably C₆-C₇ aryl; or C₆-C₁₂,preferably C₆-C₇ cycloalkyl.

The diurea thickeners may be obtained for example by reacting aprescribed diisocyanate and a prescribed monoamine. Preferred examplesof the diisocyanates include diphenylmethane-44′-diisocyanate. Preferredexamples of the monoamines include aliphatic amines, aromatic amines,alicyclic amines and mixtures thereof. Specific examples of thealiphatic amines include octylamine, dodecylamine, hexadecylamine,octadecylamine and oleylamine. Specific examples of the aromatic aminesinclude aniline and p-toluidine. Specific examples of the alicyclicamines include cyclohexylamine.

The component B is preferably an aliphatic urea thickener obtainedusing, among the above-described monoamines, octylamine, dodecylamine,hexadecylamine, octadecylamine or oleylamine or a mixture thereof.

The content of the thickener of the component (B) may be an amount withwhich a necessary consistency can be obtained, and is normallypreferably 1 to 30% by mass, more preferably 5 to 20% by mass based onthe total mass of the grease composition.

In general, the component (C), molybdenum disulfide, used in the presentinvention is widely used as a solid lubricant in a constant velocityjoint. In the lubrication mechanism thereof, it is known to have a layerlattice structure which is easily delaminated due to slide motion todecrease frictional resistance. It is also effective for prevention ofseizing of a constant velocity joint.

The content of the component (C) is preferably 0.1 to 10% by mass, morepreferably 0.5 to 5% by mass based on the total mass of the greasecomposition.

Specific examples of the component (D), molybdenumdialkyldithiocarbamate, used in the present invention include thoserepresented by the following General Formula (2).

[R³R⁴N—CS—S]₂—Mo₂O_(m)S_(n)  (2)

wherein R³ and R⁴ represent each independently C₁-C₂₄, preferably C₂-C₁₈alkyl; m represents 0 to 3; n represents Ito 4; and m+n=4.

The content of the component (D), molybdenum dialkyldithiocarbamate, ispreferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass basedon the total mass of the grease composition.

Examples of the component (E), zinc dithiophosphate, used in the presentinvention include those represented by the following General Formula(3).

wherein R⁵ represents C₁-C₂₄ alkyl or C₆-C₃₀ aryl, preferably C₁-C₅alkyl.

The content of the component (E), zinc dithiophosphate, is preferably0.1 to 10% by mass, more preferably 0.5 to 5% by mass based on the totalmass of the grease composition.

In addition to the above components, additives normally used for agrease composition, such as other extreme pressure additives,antioxidants, rust inhibitors and corrosion inhibitor, may be includedin the grease composition of the present invention.

Examples of a constant velocity joint wherein the torque transmissionmember of the constant velocity joint of the present invention isspherical include fixed type constant velocity joints such as those ofthe Rzeppa type, Birfield type and the like and sliding type constantvelocity joints such as those of the double offset type, cross groovetype and the like. These have a structure wherein a ball is used as thetorque transmission member, which ball is arranged on tracks formed onan outer race and an inner race of the constant velocity joint andincorporated via a cage.

Examples of a constant velocity joint wherein the constant velocityjoint of the present invention is a fixed type constant velocity jointinclude the above mentioned fixed type constant velocity joints such asthose of the Rzeppa type, Birfield type and the like.

Examples of a constant velocity joint wherein the constant velocityjoint of the present invention is a plunging type constant velocityjoint include the above mentioned plunging type constant velocity jointssuch as those of the double offset type, cross groove type and the like,which may be at an operating angle while being capable of slidingaxially.

EXAMPLES

The present invention will now be described in more detail by way ofExamples.

Examples 1-4, Comparative Examples 1-8 Preparation of Grease Composition

In a container, 1050 g of the base oil and 294.3 g ofdiphenylmethane-4,4′-diisocyanate were added and heated to 70 to 80° C.In a separate container, 460 g of the base oil and 605.7 g ofoctadecylamine were added and heated to 70 to 80° C., which resultingmixture was then added to the above container, followed by allowing thereaction for 30 minutes with thorough stirring. The resulting reactionproduct was allowed to cool to obtain a base urea grease. To this baseurea grease, additives were added according to the formulations shown inTables 2 to 4, and the base oil was appropriately added thereto,followed by adjusting the obtained mixture to the No. 1 grade of theconsistency by a 3-roll mill.

Evaluation (1) Viscosity of Base Oil

Measurement in accordance with JIS K 2283.

Viscosity of the base oil at 100° C. was measured.

(2) Low-temperature Torque (−40° C.)

Measurement in accordance with JIS K 2220 18.

The starting torque at −40° C. was measured.

The evaluation criterion is as follows.

Starting torque: less than 1000 mN · m Good ◯ 1000 mN · m or more Bad X

(3) Boot Resistance

Measurement in accordance with JIS K 6258.

Volume change at 120° C. for 72 hours was measured.

The evaluation criterion is as follows.

Boot 0 to less than + 5% Good ◯ resistance: 0% or less, or + 5% or moreBad X

(4) SRV Friction Coefficient

Test piece Ball Diameter 10 mm (SUJ-2) Plate Diameter 24 mm × 7.85 mm(SUJ-2) Test Load 500 N condition Frequency 40 Hz Amplitude 1500 μm Time60 minutes Test temperature 150° C. Measurement The average of thefriction coefficients during the last 5 item minutes.

(5) Heat Release Test (Temperature Control Performance)

Test conditions Rotation speed 6000 rpm Torque 200 Nm Joint angle 3°Operating time 100 h Joint type Cross groove type joint Measurement itemSurface temperature of the outer race of the joint

The evaluation criterion is as follows.

Temperature control performance:

Joint temperature less than 120° C. Good ◯ Joint temperature 120° C. ormore Bad X

Raw materials and formulations of the base oils used in Examples andComparative Examples are shown in Table 1.

TABLE 1 Type of oil Alcohol Carboxylic acid Note Ester synthetic oil (a)Isodecyl alcohol Trimellitic acid Present invention Ester synthetic oil(b) 2-Ethyl-1- Trimellitic acid Present invention hexanol Estersynthetic oil (c) 1-Octanol Trimellitic acid Present invention Estersynthetic oil (d) 2-Octyldodecanol Pyromellitic acid Present inventionEster synthetic oil (e) Dipentaerythritol 2-Ethylhexanoic acidComparative Example Ester synthetic oil (f) Pentaerythritol Octanoicacid Comparative Example Synthetic hydrocarbon oil (g) Poly-α-olefinPresent inventionMoDTC: molybdenum dialkyldithiocarbamate (In Formula 2, R³ and R⁴represent C₄ alkyl, m represents 0 to 3, and n represents 1 to 4.)ZnDTP: zinc dithiophosphate (In Formula 3, R⁵ represents C₃-C₆ alkyl.)Formulation ingredients and evaluation results of the greasecompositions of the Examples and the Comparative Examples are shown inTables 2 to 4. The number in parentheses in the line of each base oilcomponent in Tables 2 to 4 represents % by mass of the component in thebase oil.

TABLE 2 Example 1 Example 2 Example 3 Example 4 A. Base oil 81 81 81 81Ester synthetic oil (a) (20) Ester synthetic oil (b) (20) Estersynthetic oil (c) (20) Ester synthetic oil (d) (20) Ester synthetic oil(e) Ester synthetic oil (f) Synthetic hydrocarbon (80) (80) (80) (80)oil (g) B. Thickener 15 15 15 15 C. MoS₂   2.5   2.5   2.5   2.5 D.MoDTC   0.5   0.5   0.5   0.5 E. ZnDTP   1.0   1.0   1.0   1.0 Viscosityof base oil   32.0   29.4   31.2   35.6 Low-temperature torque Starting560  680  610  660  Running 290  380  300  320  Boot resistance,   +2.0  +2.6   +3.1   +2.4 Volume change SRV friction coefficient    0.05   0.05    0.05    0.05 Temperature control 110  102  104  108 performance, joint temperature Low-temperature ◯ ◯ ◯ ◯ performance Bootresistance ◯ ◯ ◯ ◯ Temperature control ◯ ◯ ◯ ◯ performance

TABLE 3 Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 A. Base oil 81 81  81  81 Ester syntheticoil (a) Ester synthetic oil (b) Ester synthetic oil (c) (100) Estersynthetic oil (d) Ester synthetic oil (e) (10) Ester synthetic oil (f)(20) Synthetic hydrocarbon oil (g) (90) (80) (100) B. Thickener 15 15 15  15 C. MoS₂   2.5   2.5    2.5    2.5 D. MoDTC   0.5   0.5    0.5   0.5 E. ZnDTP   1.0   1.0    1.0    1.0 Viscosity of base oil   33.3  28.0    9.6   40.7 Low-temperature torque Starting 1300<  1300<  540680 Running —*⁵ —*⁵ 200 350 Boot resistance, Volume change   −5.2   +2.3  +12.1   −9.2 SRV friction coefficient    0.05    0.05    0.12    0.13Temperature control performance, 106  106  — — joint temperatureLow-temperature performance X X ◯ ◯ Boot resistance X ◯ X X Temperaturecontrol performance ◯ ◯ X X

TABLE 4 Comparative Comparative Comparative Comparative Example 5Example 6 Example 7 Example 8 A. Base oil   83.5   83.5   83.5   83.5Ester synthetic oil (a) Ester synthetic oil (b) (20) Ester synthetic oil(c) (100) (20) (20) Ester synthetic oil (d) Ester synthetic oil (e)Ester synthetic oil (f) Synthetic hydrocarbon oil (g) (80) (80) (80) B.Thickener  15 15 15 15 C. MoS₂  0  0  0  0 D. MoDTC    0.5   0.5   0.5 0 E. ZnDTP    1.0   1.0   1.0  0 Viscosity of base oil   29.4   29.4  29.4   29.4 Low-temperature torque Starting 730 720  750  690  Running370 300  350  320  Boot resistance, Volume change   +10.7   +1.4   +2.1  +3.0 SRV friction coefficient    0.16    0.08    0.07 SeizingTemperature control performance, — — — — joint temperatureLow-temperature performance ◯ ◯ ◯ ◯ Boot resistance X ◯ ◯ ◯ Temperaturecontrol performance X X X X —*⁵: Incapable of measuring the rotationaltorque since the starting torque was too high (1300<) at lowtemperature.

Results

As seen from the results, the grease compositions of Examples 1 to 4 ofthe present invention for a constant velocity joint, wherein a base oil(A) containing 10 to 95% by mass of an ester synthetic oil produced froman aliphatic alcohol and an aromatic carboxylic acid and 90 to 5 weightpercent of a synthetic hydrocarbon oil is used and the components (C) to(E) are included as additives, are excellent in low-temperatureperformance, boot resistance and temperature control performance andshow low friction coefficients.

In contrast, Comparative Example 1, wherein an ester synthetic oilproduced from an aliphatic alcohol and an aliphatic carboxylic acid wasused instead of the component (A) of the present invention, shows poorerlow-temperature performance and boot resistance.

Comparative Example 2 of the present invention which does not containthe component (A) shows poorer low-temperature performance.

Comparative Examples 3 and 5 wherein only an ester synthetic oil wasused as the base oil shows poorer boot resistance and temperaturecontrol performance.

Comparative Example 4 wherein only a synthetic hydrocarbon oil was usedas the base oil shows poorer boot resistance and temperature controlperformance.

Comparative Examples 6 to 7 which do not contain molybdenum disulfideshow poorer temperature control performance.

Comparative Example 8 which does not contain MoDTC and ZnDTP showspoorer temperature control performance and causes seizing.

1. A grease composition for a constant velocity joint, which greasecomposition comprises the following components (A) to (E): (A) a baseoil containing 10 to 95% by mass of an ester synthetic oil produced froman aliphatic alcohol and an aromatic carboxylic acid and 90 to 5% bymass of a synthetic hydrocarbon oil; (B) a thickener; (C) molybdenumdisulfide; (D) molybdenum dialkyldithiocarbamate; and (E) zincdithiophosphate.
 2. The grease composition for a constant velocityjoint, according to claim 1, wherein the synthetic hydrocarbon oil ofthe component (A) is a poly-α-olefin.
 3. The grease composition for aconstant velocity joint, according to claim 1, wherein the estersynthetic oil of the component (A) is produced from a C₆-C₂₂ aliphaticalcohol and a C₈-C₂₂ aromatic carboxylic acid having 2 to 6 carboxylgroups.
 4. The grease composition for a constant velocity joint,according to claim 1, wherein the thickener of the component (B) is aurea compound.
 5. The grease composition for a constant velocity joint,according to claim 1, wherein each of the contents of molybdenumdisulfide of the component (C), molybdenum dialkyldithiocarbamate of thecomponent (D) and zinc dithiophosphate of the component (E) is 0.1 to10% by mass based on the total mass of the grease composition.
 6. Aconstant velocity joint wherein the grease composition according toclaim 1 is filled.